9 pin miniature preamp tube (Amplification Factor =100). This is the ubiquitous Chinese 12AX7 with premium selection. The gain is high and the German Tube Amp Doctor must be filtering out the noisiest ones. Premium selected by Tube Amp Doctor, this is a quiet Chinese 12AX7 with high gain that will bring a dull sounding amp back to life. For more information about our 12AX7 tubes, see our tech corner article on 12AX7s.